Astronomy: Comets - mesmerising celestial wonders

How did you get into astronomy? You may have been a witness to one of many celestial events that may have left you in awe and wonder.

It could be an eclipse, or a meteor shower, or a view of Saturn through a telescope, but for many, like myself, it was the apparition of a bright comet.

My introduction to Halley’s Comet in April, 1986 wasn’t exciting visually, although it was significant.

If it wasn’t for Halley’s Comet I may never have pursued the hobby.

Comet C/2006 P1 McNaught: The head of the comet was obscured by bushfire smoke, but the tail appeared majestically above in all its glory. Photo Chris Wyatt

From light polluted Western Sydney I witnessed some other notable bright comets like Hyakutake and Hale-Bopp.

Once in a lifetime: Comet C2006P1 McNaught in moonlight, January 2007. Photo Chris Wyatt

Then, when I moved to country dark skies, I began to follow some fainter, lesser known comets conducting visual observations, continuing the tradition like many comet watchers before me had done, and I found the history particularly exciting.

The sight of a bright comet with a long tail appearing suddenly in the evening or morning sky, seemingly out of nowhere, left long lasting memories and brought wonder and terror.

They were referred to as “Great” comets. Great comets have been recorded throughout ancient history right up to the present day, even commemorated on ancient coins and various forms of artwork.

The mystery of comets have been troubling scientists for centuries.

Today we know that comets are small fragile bodies composed mainly of ice and dust, and becomes heated by the Sun on its orbital journey through the inner solar system.

The ices sublimate and drag tiny dust particles with the gas released from the nucleus to the surrounding region producing the ‘coma’, and shrouds the nucleus from view.

The coma is what betrays a comet’s presence to observers on Earth initially, a fuzzy globule of light slowly moving against the background of stars.

Comets produce gas and dust in varying quantities, so these tails (gas and dust) stream away from the coma creating their characteristic appearance.

As the comet nears the Sun the ratio of gas and dust produced by increasing activity on the nucleus can change dramatically.

To observers on Earth this affects the apparent brightness of a comet and hence its visibility. Many other factors need to combine to make a comet ‘Great’ and memorable in its appearance.

In 2007, comet C/2006 P1 McNaught became one of the brightest comets ever seen. The timing was impeccable!

This comet made its closest approach to the Sun well inside the orbit of Mercury. The intense heat drove dust activity to incredible levels, sunlight scattering off dust particles in the tail enhanced the appearance of the comet and resulted in this spectacular display.

It turned into one of the grandest sights the heavens could offer.

To this day Comet McNaught remains the brightest one seen since 1965 and it’s a view forever etched in my memory.